DeFelsko PosiTector SPG v.1.1 Quick Guide - Manual (Page 4)

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The factory zero setting may not always be precise,
particularly after a probe tip exchange. For best accuracy, the
gage should be zeroed on the included glass plate.
1.Select from the menu.
2.Press the (+) button to select the number of readings to be
used to obtain an average, typically 3.
3.Repeatedly measure the glass plate. After the last
measurement, the gage will calculate a Zero which represents
the average of all the Zero readings taken.
Glass Plate Zero
Setting the Gage to zero on the glass plate is the preferred zero
adjustment method:
Factory Zero
If a glass plate or suitable smooth, hard surface is not available,
the factory zero setting can be restored:
1. Select from the menu.
2. Press the down button to select “Reset” and press the center
navigation button. xxxx The factory calibration icon iiiii will
appear on the LCD.
Zero
NOTE:
Zero
The PosiTector SPG has only one adjustment point at zero. The
zero point can be set using one of two methods. Both methods are
found under the Zero menu option.
Zero Menu Zero Menu
Zero
If not, see Returning for Service (pg. 9). Metric example: gage
tolerance is ±5% or ±5 µm whichever is greater. The 76 µm shim
tolerance is ±5 µm. So the average of several measurements
should be between 66 and 86 microns. Inch example: gage
tolerance is ±5% or ±0.2 mils whichever is greater. The 3 mil shim
tolerance is ±0.2 mils. So the average of several measurements
should be between 2.6 and 3.4 mils.